1. Field of the Invention
The present invention relates to mammography devices and techniques.
2. Description of the Prior Art
Tomosynthesis represents an extension of classical two-dimensional mammography. For example, a set of 25 x-ray images is created. To obtain these x-ray acquisitions, the x-ray tube is moved on an orbit in a circle segment between +25 and −25 degrees, starting from a perpendicular line set up on the detector surface. X-ray radiation from the x-ray source is then triggered at regular intervals, and the respective x-ray image is read out by the detector and buffered. With a tomosynthesis reconstruction algorithm, a volume set is subsequently created from the multiple projections that are present in digital image data. Depending on the algorithm, a calculation of the digital x-ray image data read out from the detector takes place during or after the conclusion of the x-ray acquisitions. Tissue variations can be localized in the volume set. Tissue variations of different size in a breast are projected differently onto the detector at varying projection angles. During the subsequent reconstruction—for example with the method of filtered back-projection—tissue structures in the breast are enhanced by suitable filtering, displacement and summation. The reconstruction leads to a series of slice images at different depth levels parallel to the detector surface. An analysis of the reconstruction result normally takes place in Z-slices of the volume set that are situated parallel to the detector. The reconstructable tomosynthesis volume is affected by the detector size and deflection of the x-ray head. Given a large deflection of the x-ray head, a better depth resolution can be achieved at the cost of a reduction in size of the reconstructable volume. Given a smaller deflection of the x-ray head, the reconstructable volume increases in size but the depth resolution is correspondingly reduced.
In the creation of a volume set it can occur that the reconstructed volume is smaller than the actual, compressed breast region. This has the disadvantage that no diagnosis can be made with regard to the breast tissue in the border region of the image.